A bipolar junction transistor (BJT) is a type of transistor that relies on the contact of two types of semiconductor for its operation. BJTs may be used as amplifiers, switches, or in oscillators, for example. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across a junction between two regions of different charge concentrations. The regions of a BJT are called emitter, collector, and base. A discrete transistor has three leads for connection to these regions. By design, most of the BJT collector current is due to the flow of charges injected from a high-concentration emitter into the base where there are minority carriers that diffuse toward the collector, and so BJTs are classified as minority-carrier devices.
Because of the known temperature and current dependence of the forward-biased base-emitter junction voltage (VBE), the BJT can be used to measure temperature by subtracting two VBE voltages at two different bias currents in a known ratio. The voltage difference (ΔVBE) is proportional to absolute temperature (PTAT) of the BJT device.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.